Using Multi-spectral Imagery to Help Fight Fires
By Jennifer Hintz

Much of the western part of the state of Montana was on fire. More than two million acres of forest were closed to the public, for fear that a stray cigarette butt or overheated auto exhaust pipe might ignite the remaining portion of unburned meadows or forests. Roads were closed, and those who remained in the area described it as "eerie." There was a strong sense of urgency. Professionals from throughout the country were called in to help at every level, from fighting fires at flame fronts to providing GIS services and producing daily fire-progress maps. Anyone who helped with the fire fighting effort was considered something of a hero, given free passes to ball games or concerts in the rare hours when they were not working. "When I told people that I was helping map fires at the fire lab, they just told me to go on in to the ball park," reported Paul Olson of the Minnesota DNR, who was stationed in Missoula for 17 days to help in the GIS department. "A group of fire fighters even got a standing ovation at a Willie Nelson concert."
      It became increasingly obvious in late August, as flames covered large tracts of Montana and vast areas were blanketed in smoke, that more help was needed. What was desperately needed was a method to see through the expansive smoke, to detect flame fronts and hot spots on the ground, and to generate accurate coordinates of the fires, relaying this information rapidly enough to make a difference to fire fighters out in the field. This is not a new requirement. Satellite and airborne data have been used in the past to successfully manage fires, but here the need was threefold: first, to be able to see where the flame fronts were located in reference to ground features, whether during the day or at night; second, to define on the fly very accurate coordinates for flame fronts; and third, to be able to access this data almost immediately after flight.
      Airborne Data Systems Inc., a small company in southwestern Minnesota that manufactures airborne digital, multi-spectral imaging systems, believed that they had the answers to these problems. When the call came to provide their imaging system for a major fire situation, company representatives boarded one of their Piper Seneca twin-engine airplanes and flew to Missoula, Mont., to work with fire experts from the U.S. Forest Service, the University of Montana, and the Missoula Fire Lab.

Preparing for Flight
Prior to the fire outbreak, a team of researchers from the University of Montana had been working with satellite data to create models for predicting fire behavior. As the disaster heightened, demand for these models increased, as did the need for high-resolution imagery that could be rapidly disseminated to fire managers. What began as a research project, designed to be implemented some years down the road, turned into an emergency response effort. "It simply became a point of delivering all the help we could," said Lloyd Queen, a research team member and associate professor of forestry at the University of Montana (Missoula).
      Colin Hardy, a research forester at the Forest Service's Fire Science Lab, arranged for the demo. In preparation for the test, Hardy and Queen visually verified fire locations by using a hand-held GPS device while flying over target areas. This was no easy task given the prevalence of thick smoke, but they were able to obtain reasonably accurate estimates of fire locations. These GPS coordinates were used that very afternoon to develop a flight plan for Airborne Data Systems, for the purpose of acquiring data in the air by using the company's Spectra-View® five-band, multi-spectral digital imaging system.

The System
This imaging system has several features that lend themselves to this sort of task. First, the five-band system contains both a thermal detector that captures data in the three- to five-micron range, as well as four other detectors equipped with filters in the visible and near-infrared range. Fire can be detected during daylight or nighttime hours - with the added benefit of some background imagery during the day - and captured with the near-infrared band, with complete background imagery displayed in true color (RGB) if smoke has not obstructed the view. Second, these systems are equipped with a precision Inertial Measurement Unit (IMU). This system integrates images with coordinates and other aircraft attitude data gleaned from the IMU such as roll, pitch and yaw, meaning that images can be precisely geo-referenced as soon as the data is processed into a viewable format. By extrapolation during processing, each pixel in an image is assigned coordinates in either latitude/longitude or UTM values, so flame fronts and hot spots can be precisely located on the ground. It has been proven during testing that scene centers are within six meters of their true ground position. The third major advantage of using a Spectra-View® system for fire fighting is that imagery is in a completely digital format, from acquisition to delivery. No scanning is involved, which saves precious time in circumstances where time is crucial, both in saving money and in preserving one of Montana's most valuable resources-its wilderness.

The Flight
After several hours of flying time the first day, raw data was taken back to the lab via a removable hard drive, to be processed into geo-referenced images. One of the major values of the Spectra-View® system quickly became apparent. Data was viewable within about 20 seconds per scene, and precise coordinates of any feature could be immediately determined. Experts at the fire lab assessed the data for flame fronts by viewing a combination of near-infrared and thermal bands that penetrated the thick smoke clouding all the features in the visible bands. This band combination dramatically illuminated the fire itself in a bright yellow color, while vegetation and other ground features appeared dark blue. A double-click of the mouse anywhere in the scene revealed specific coordinates for any desired area. Phase I of the project was complete: obtaining precise coordinates of flame fronts and quickly relaying this data to fire fighters in the field. Under these circumstances "precise" meant "within several meters of true ground coordinates," while "quickly" meant "within hours, or potentially even minutes" of the flight.
      Phase II of the project, mapping fire position and movement, involved GIS personnel from the Fire Lab. GIS staff mosaicked true-color imagery by using ERDAS IMAGINE® to provide the backdrop. Vector drawings outlined fire areas that were visible in the thermal band. Finally, maps were produced that included perimeters and coordinates of active fire areas and residual hot spots, as well as the direction of fire movement and the distance between fires. This new methodology enabled useful data to be placed into the hands of people who could use it to quickly make educated decisions. "We were able to use the data to make rapid decisions about which communities to protect," said Hardy.
      Subsequent flights were performed over several days to detect movement of the fires. Because these images have such tight geo-referencing, it was a simple task to overlay images from one day over those of the previous day in GIS software, thus creating an accurate account of fire movement over time. The implications for this process are extensive. Magnitude of damage can be quickly assessed, and efforts can be made to protect sensitive areas lying within the fire's path. In concert with atmospheric data, fire behaviorists can study fire movement and produce models to predict future fire conduct.

The Future of Airborne Multi-spectral Digital Imagery
This project highlighted the rapid applications of digital multi-spectral imagery. However, this type of imagery offers a myriad of further applications as well, many of which can be of great use for assessing damage and post-fire recovery, and for general natural resources management. Damage can be easily measured and mapped since it is a relatively simple task to locate and measure the size of burned areas. Vegetation indices can be used to determine the health and welfare of surviving vegetation, as well as regrowth in burned areas. By taking advantage of several GIS software capabilities, including auto-classification and more sophisticated trained classification, land-cover/land-use analyses are more easily achieved. Knowledge of spectral signatures of given species can aid in supervised classification of data, and in individual species recognition for timber inventories.
      Airborne imagery offers the added benefit of tasking an aircraft specifically for a job, and of providing high-resolution data. Individual trees are visible, allowing for decision-making on a small scale as well as on a full-forest scale.
      The utility of data increases with the education level of the end-user. Many users have reached a point where digital multi-spectral data is not foreign to them. With the prevalence of satellite data and other airborne imaging systems, employees of many businesses and institutions have become well educated in the use of multi-spectral digital data. Precision has increased and, with post-processing, digital imagery becomes competitive with traditional film as to accuracy. Multi-spectral digital orthophotos have been in demand by the industry, and they are now much more easily produced, either through production houses or through the use of commercial, off-the-shelf software.
      With a successful demonstration under their belts of the five-band Spectra-View® system as employed in a major fire event, Airborne Data Systems hopes that others in the industry will gain confidence to use new technology in disaster management. The company has been manufacturing imaging systems for eight years, concentrating on building and selling systems rather than in acquiring data. "We don't want to compete with our customers for acquisition business, but we do like to demonstrate the system whenever possible," said David Fuhr, the company's president and CEO. Airborne Data Systems is actively involved in research and development to improve system function, especially in delivering accurate data to the end-user more quickly. The company's current project involves developing an air-to-ground downlink to further reduce the time from image acquisition to ground processing.

Summary
With the great number of fire disasters this past year, officials have begun to search for alternative methods of detecting fires during any time of day or night, and to quickly relay that information to field personnel. Airborne multi-spectral, digital data provides many advantages in fire detection, speed, ease of use, and information content. While it may not totally replace traditional film or satellite data in all areas, this technology shows great potential for providing quick response as well as damage assessment and management.

About the Author:
Jennifer Hintz is a GIS and applications specialist for Airborne Data Systems Inc., Wabasso, Minn. She may be reached by telephone at 507-984-5419, or via e-mail at [email protected].

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